chore(hardening): tighten security and footprint defaults

.github/workflows/check.yml

@@ -111,6 +111,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
 
       # Cache the Cargo target dir + registry per OS so the heavy
       # whisper-rs-sys C++ build only happens on a clean cache.
@@ -128,12 +130,24 @@ jobs:
       - name: cargo check (workspace)
         run: cargo check --workspace --all-targets
 
+      - name: cargo fmt
+        run: cargo fmt --all -- --check
+
+      - name: cargo clippy
+        run: cargo clippy --workspace --all-targets -- -D warnings
+
       # Library tests only — no runtime/GPU deps. Linux-gated to keep
       # the macOS + Windows legs focused on compile coverage.
       - name: cargo test (workspace, libs)
         if: matrix.os == 'ubuntu-22.04'
         run: cargo test --workspace --lib
 
+      - name: cargo audit
+        if: matrix.os == 'ubuntu-22.04'
+        run: |
+          cargo install cargo-audit --locked
+          cargo audit
+
   frontend:
     name: svelte build + lint
     runs-on: ubuntu-22.04
@@ -150,6 +164,9 @@ jobs:
       - name: Install JS deps
         run: npm ci
 
+      - name: npm audit
+        run: npm audit --audit-level=high
+
       # `tauri build` inside check.yml would trigger the full Rust build
       # which is owned by the rust job. Here we only validate that the
       # Svelte/Vite frontend compiles cleanly.